52 ANTS. 



remain distinct and lie in their respective segments even in the adult 

 ant. The first ( mediary ) and second abdominal ganglia, however, are 

 drawn up into the metathorax and fused with the metathoracic ganglion, 

 and the ganglion of the third abdominal segment comes to lie in the 

 petiole (second abdominal segment) (Fig. 13, ay"- ). The fourth, fifth, 

 sixth and seventh abdominal ganglia retain their independence, but the 

 latter two are close together and are immediately succeeded by the fused) 

 eighth to tenth, which constitute a single ellipsoidal mass, terminating 

 the chain and in the adult ant lying some distance in front of the pos- 

 terior end of thegaster (Fig. 13, ag 8 ' 11 ). The central nervous system of 

 the adult ant therefore presents only eleven ganglionic masses, formed 

 by condensation of the primitive nineteen. For convenience in descrip- 

 tion, this system may be divided into the brain and ventral cord, and 

 these, with their ganglia and peripheral nerves, may be briefly consid- 

 ered before we take up the sympathetic nervous system and the sense 



organs. 



The Brain. I agree with those authors, who, following Rabl- 

 Riickard ( 18/5 ), restrict the term " brain " to the supraoesophageal gan- 

 glion, although it must be admitted that in ants and other Hymenoptera 

 the circumcesophageal connectives are so short and robust that the 

 supra- and suboesophageal ganglia seem to form but a single mass per- 

 forated by the gullet. Leydig called this whole mass the brain ; Janet 

 suggests for it the term " encephalon." The three primitive pairs of 

 ganglia, constituting the proto-, cleuto- and tritocerebrum, though inti- 

 mately fused, can still be recognized in the adult brain, at least by their 

 innervations, but the three apparent segments indicated by the outline 

 of the organ do not correspond to the primitive segments. The proto- 

 cerebrum is the largest single pair of ganglia in the central nervous 

 systems and differs markedly from all the others in form and com- 

 plexity of structure. It is broadest in the middle where it is continued 

 on each side into the optic nerves (Figs. 28-30, on) to the compound 

 eyes. The portion between the optic nerves may be called the mid- 

 protocerebrum. It is flanked on each side by an optic ganglion (og} 

 of complicated structure and projects anteriorly as a pair of rounded 

 frontal lobes (f>b ). From the notch between these, nerves are given off 

 to the three stemmata. or ocelli (oc), when these organs are present. 

 As the median stemma has two nerves, it must have been a paired struc- 

 ture originally. The deutocerebrum is represented by a pair of rounded 

 protuberances known as the olfactory lobes (o/), which are morpho- 

 logically behind, though apparently somewhat in front of the other brain 

 segments. According to Janet, each antenna is supplied with six nerves 

 which arise close together from each olfactory lobe (Fig. 27). These 



